JPH11100274A - Silicon nitride sintered compact, its production and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high thermal conductivity by containing a specific quantity of each Si3 N4 and one or more kinds of Y and lanthgoid group elements expressed in terms of oxide, specifying the ratio of SiO2 /(SiO2 +oxide of lanthanoid element) calculated from oxygen quantity and controlling total content of Al, Be and Li to equal to or below a specific value. SOLUTION: The Si3 N4 based sintered compact contains 90-99 mol.% Si3 N4 and 1-10 mol.% one or more kinds of Y and the lanthanoid elements expressed in terms of oxide and the molar ratio of SiO2 /(SiO2 +oxide of lanthanoid group elexaent or the like) is 0.05-0.5 when the remaining quantity of oxygen substracting the quantity of the oxygen of Re2 O3 obtained by calculating the lanthanoid group elemens into oxide from the total oxygen quantity is expressed in teas of SiO2 and total content of Al, Be and Zr is <=2000 ppm. The sintered compact is >=95% in the density, 0.5-3 μm in the average particle diameter of β-type Si3 N4 particle, >=70 W/(m.k) in the heat conductivity, ∞500 MPa in the three point bending strength and ∞6 MPa.m<1/2> in fracture toughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be used as a material for various structural components used in a wide range of fields such as semiconductor substrates, automobiles, machinery and the like, and has excellent mechanical properties such as strength and fracture toughness. The present invention relates to a silicon nitride sintered body having excellent heat dissipation characteristics such as thermal conductivity and a silicon nitride circuit board using the same.

[0002]

2. Description of the Related Art A silicon nitride-based sintered body (hereinafter, also simply referred to as silicon nitride ceramics) is a material which is chemically stable at ordinary and high temperatures and has excellent mechanical properties. It is a material suitable as a sliding member or the like. It is also used as an electrical insulating material by utilizing high insulating properties.

[0003] However, silicon nitride is a substance having a strong covalent bond and has excellent high-temperature characteristics, but is a substance which is difficult to be sintered. For this reason, silicon nitride ceramics are added with an oxide such as Y ₂ O ₃ as a sintering aid to increase the sinterability and make the ceramics denser. These sintering aids and SiO ₂ contained in the silicon nitride powder as a raw material form a grain boundary phase of the silicon nitride ceramics, and affect mechanical and thermal properties.

[0004] As described above, conventional silicon nitride ceramics are obtained by adding a sintering aid to silicon nitride powder, molding the resultant, and firing the obtained molded body at a high temperature of 1600 ° C to 2200 ° C for a predetermined time. It is manufactured by grinding the obtained sintered body into a desired shape.

[0005] On the other hand, a substrate for a semiconductor circuit is required to have high thermal conductivity so as to obtain excellent heat dissipation characteristics in addition to electric insulation. Conventionally, alumina (A
l ₂ O ₃ ) A conductive metal circuit layer is joined to the surface of a ceramic substrate having excellent insulation properties, such as a sintered body, with a brazing material, and a semiconductor element is mounted on a predetermined position of the metal circuit layer. Circuit boards are widely used.

In recent years, as circuit boards have become smaller and semiconductor elements have become more highly integrated, it has been desired to improve the heat radiation characteristics of insulating materials in these circuit boards. As such a material, silicon carbide (SiC) and aluminum nitride (AlN) to which BeO is added have been developed. However, Si
C and AlN have high thermal conductivity, but have low mechanical properties such as strength and fracture toughness, and thus have problems in heat cycle characteristics and handling strength.

[0007] Silicon nitride sintered bodies are excellent in mechanical properties such as strength and fracture toughness, and thus are being applied to structural materials. However, they have low thermal conductivity compared to SiC and AlN. However, it has not been sufficiently applied to an electrical insulating substrate requiring high heat radiation characteristics. The reason that the thermal conductivity of silicon nitride is low is that a part of the sintering aid component added to densify silicon nitride is dissolved in silicon nitride grains or is ubiquitous in grain boundaries. This is because phonons (mechanisms for transferring heat in ceramics) are scattered. For example, in a sintered body to which Y ₂ O ₃ and Al ₂ O ₃ , which are general sintering aids, are added, the thermal conductivity is about 20 W / (m · K).

When Al and oxygen are present in the silicon nitride particles, a sialon is locally formed, and the thermal conductivity of the sialon is extremely low. Therefore, a silicon nitride sintered body using an Al-based sintering aid is used. Thermal conductivity will be low. Since silicon nitride is an electrically insulating material, heat is carried by phonons. Since phonons are scattered by lattice disorder, grain boundary phase, pores, etc., the thermal conductivity of silicon nitride also depends on the crystal structure of silicon nitride, the type of sintering aid, and the solid solution in the crystal grains. receive. The ideal thermal conductivity of silicon nitride is estimated to be 200 W / (m · K) or more based on the composition, crystal structure, etc., but a silicon nitride single crystal is actually synthesized and applied to practical use. It is difficult to do so, and is generally manufactured as a sintered body.

The sintering of silicon nitride proceeds while the silicon nitride particles dissolve and precipitate in a liquid phase comprising a sintering aid and a SiO ₂ component contained in the silicon nitride raw material powder. Individual silicon nitride particles in the body are close to a single crystal,
Although relatively high thermal conductivity is expected, in the actual silicon nitride sintered body, the influence of the solid solution of the impurities in the grain boundary phase and silicon nitride grains described above is larger, and the usual manufacturing conditions According to the above, in reality, only about 10 to 20% of the theoretical thermal conductivity can be obtained.

[0010] For this reason, the high thermal conductivity of a silicon nitride sintered body has been described in the academic journal of the Ceramic Society of Japan, January 1989.
As described in Monthly Pages 56 to 62, HI was obtained by adding only Y ₂ O ₃ without using a sintering aid containing Al.
P (hot isostatic pressure) sintering results in a thermal conductivity of 70
A sintered body of W / (m · K) is obtained.

Further, as described in JP-A-4-175268 and JP-A-4-219371, the content of Al and oxygen in the sintered body is reduced, and the content of Ti and Z is reduced.
By adding metals such as r and Hf, and optionally adding Y ₂ O ₃ as a sintering aid, a thermal conductivity of 40 W /
A method for obtaining a sintered body of (m · K) or more is known.

Further, The Ceramic Society of Japan 1
In 996, January, pp 49-53, using a small amount of Y ₂ O ₃ and Nd ₂ O ₃ as a sintering aid, 2200 ° C. and a very high temperature for 4 hours, by HIP sintering, heat A silicon nitride sintered body having a conductivity of 100 W / (m · K) or more is obtained.

[0013]

SUMMARY OF THE INVENTION Conventionally known SiC, BeO,
AlN has a high thermal conductivity of 100 W / (m · K) or more and is excellent in heat radiation properties, but has low mechanical properties such as strength and fracture toughness. Therefore, when used as a circuit board or the like, the ceramic substrate near the joint with the metal circuit layer is liable to crack due to damage in the mounting process or repeated thermal cycling accompanying the operation of the semiconductor element, and heat resistance There was a problem that cycle characteristics and reliability were low.

Although conventional silicon nitride ceramics have excellent mechanical properties such as strength and fracture toughness, their thermal conductivity properties are, as described above, SiC and Be.
In order to obtain a material having a lower thermal conductivity than O and AlN ceramics, and a material having a high thermal conductivity, a special sintering such as HIP sintering at a high temperature using a high-purity raw material powder containing few impurities such as Al is used. It is necessary to use the method, and the obtained sintered body is very expensive, and at present, it is hardly practically used for electronic materials such as circuit boards for semiconductors.

The present invention has been made in view of the above-mentioned circumstances, and has excellent strength, fracture toughness, excellent mechanical properties, and excellent heat conduction properties. It is an object of the present invention to provide inexpensively a silicon nitride sintered body that is excellent in characteristics and reliability and is suitable as a material for automotive parts such as semiconductor circuit boards and valves.

[0016]

Means for Solving the Problems To achieve the above object, the present inventor has set forth the powder characteristics of the raw material powder, the composition and amount of the sintering aid, and the sintering aid for obtaining a silicon nitride based sintered body. As a result of intensive studies on the bonding conditions and the like, a silicon nitride based sintered body having excellent mechanical properties such as strength and fracture toughness and having a significantly higher thermal conductivity than conventional ones was obtained, and the present invention was completed. It is a thing.

That is, the silicon nitride sintered body of the present invention
Silicon nitride _{(Si 3 N 4) 90~99mol%} , yttrium (Y) and oxides of one or more selected from the group consisting of lanthanoid elements (Re ₂ O ₃₎ in terms of 1~10m
containing ol%, the balance excluding the amount of oxygen belonging to Re ₂ O ₃ than the total oxygen content in the sintered body when the SiO _2, S
The molar ratio of iO ₂ / (Re ₂ O ₃ + SiO ₂ ) is 0.05
To 0.5, the average particle diameter (average minor axis diameter) of the silicon nitride particles is 0.5 to 3 μm, and Al, Be and Li in the sintered body are
Is 2000 ppm or less, and the thermal conductivity is 70 W / (m · K) or more.

The silicon nitride sintered body of the present invention has a K phase (ReSi ₂ N),
Phase (Re ₄ Si ₂ O ₇ N ₄ ), H phase (Re ₁₀ Si ₇ O ₂₃
N ₄ ), Re ₂ Si ₃ O ₃ N ₄ , Re ₂ SiO ₅ and R
e ₂ O ₃ , K phase, J phase, H phase, Re phase
The total (I _GB ) of the main peak intensities of each of ₂ Si ₃ O ₃ N ₄ , Re ₂ SiO ₅ and Re ₂ O ₃ is 0 with respect to the peak intensity ( _ISN ) of the (200) plane of β-type silicon nitride. .03-
The silicon nitride-based sintered body described above is 0.20.

Further, the present invention relates to a group comprising yttrium (Y) and a lanthanoid element in 90 to 99 mol% of silicon nitride powder having a total content of Al, Be and Li of 2000 ppm or less and an α ratio of 50% or less. 1 to 10 mol% in terms of oxide of one or more, SiO ₂ of the amount of oxygen in the silicon nitride powder to the amount of SiO ₂ and addition was SiO ₂ in terms
The total quantities, the molar ratio of _{SiO 2 / (Re 2 O 3} + SiO 2) is added and mixed so that 0.05 to 0.5, 1M
In a nitrogen pressurized atmosphere of less than Pa, at a temperature of 1800 to 2000
A method for producing the silicon nitride-based sintered body, characterized in that the sintered body is fired at a temperature of ℃.

In addition, the present invention is a circuit board using the silicon nitride sintered body.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Silicon nitride ceramics have a sintered body structure in which columnar β-type silicon nitride particles are intricately entangled, and this structure greatly contributes to mechanical properties such as strength and fracture toughness. I have. Moreover, the pores in the sintered body act as defects and affect the strength characteristics. In silicon nitride ceramics, it is important to optimize the structure of the sintered body including these defects in order to obtain a sintered body having excellent mechanical properties such as strength and fracture toughness.

However, the thickness of the interface between the two particles when the silicon nitride particles in the silicon nitride sintered body are in contact with each other is about 1 nm,
This is 1/10 or less of the phonon mean free path.
From this, regarding the thermal conductivity of the silicon nitride sintered body,
It is considered that the influence of phonon scattering due to defects in the silicon nitride particles is a larger controlling factor than the influence of the grain boundary phase. Therefore, it is presumed that it is important to control the defects in the silicon nitride particles in order to improve the thermal conductivity of the silicon nitride sintered body.

Based on the above presumption, the present inventors have reduced the intragranular defects in the silicon nitride sintered body and controlled the grain boundary phase, so that the mechanical properties and heat conduction, which are the objects of the present invention, have been achieved. Based on the prediction that a sintered body excellent in both properties can be obtained, the present inventors have conducted intensive studies and, as a result, have arrived at the present invention.

That is, the silicon nitride sintered body of the present invention
Silicon nitride _{(Si 3 N 4) 90~99mol%} , yttrium (Y) and oxides of one or more selected from the group consisting of lanthanoid elements (Re ₂ O ₃₎ in terms of 1~10m
ol%. Various oxides and the like are used as a sintering aid for silicon nitride, and a conventionally known silicon nitride obtained using a sintering aid that dissolves with silicon nitride exemplified by Al ₂ O ₃ is used. In the porous sintered body, a portion in which the sintering aid such as alumina is dissolved in the silicon nitride particles is present as a defect, so that phonons are scattered and the thermal conductivity is reduced. On the other hand, the silicon nitride-based sintered body of the present invention contains one or more oxides selected from the group consisting of yttrium (Y) and lanthanoid group elements that do not form a solid solution with silicon nitride (Re _2).
The content is 1 to 10 mol% in terms of O ₃ ), preferably 2 to 5 mol%. Among the yttrium and lanthanoid group elements, Yb, E
An element having a small ionic radius such as r is preferable.

If the content of one or more oxides selected from the group consisting of yttrium (Y) and lanthanoid group elements is less than 1 mol%, the amount of liquid phase generated during sintering is insufficient, and sufficient densification is achieved. A sintered body cannot be obtained.
On the other hand, when the content of the rare earth element exceeds 10 mol%,
If the amount of the grain boundary phase is too large, the thermal conductivity is reduced due to phonon scattering in the grain boundary phase. On the other hand, if the amount of the grain boundary phase is too large, mechanical properties such as strength and fracture toughness, particularly, high-temperature strength are reduced.

Further, the silicon nitride sintered body of the present invention
Yttrium and lanthanoid elements from total oxygen in the body
At least one element selected from the group consisting of
e_TwoO_ThreeThe remainder excluding the oxygen content attributed to_Twoage
When the SiO_Two/ (Re _TwoO_Three+ SiO_Two) Mol
The ratio is from 0.05 to 0.5, preferably from 0.1 to 0.5
0.4. The sintering of silicon nitride is performed with the added sintering aid.
SiO in raw material powder and optionally added_TwoFrom
Silicon nitride particles dissolve and precipitate in the grain boundary phase (liquid phase)
Grain grows. In this case, the SiO 2 in the liquid phase_TwoIncreased
When added, silicon nitride particles, some of which precipitate from the liquid phase,
Solid solution and exist as defects in silicon nitride particles.
As a result, phonons are scattered and thermal conductivity is reduced.
U. Therefore, as the composition of the grain boundary phase, the total oxygen in the sintered body
Group consisting of yttrium and lanthanoid elements by quantity
Re converted into oxides of at least one selected from_TwoO_ThreeReturn to
The remainder excluding the oxygen content belongs to SiO_TwoThen, S
iO_Two/ (Re_TwoO_Three+ SiO_Two ) Is 0.5 or less
Lowering is effective in improving the thermal conductivity.

On the other hand, oxygen is inevitably contained in the silicon nitride powder, which is the raw material powder, and a SiO ₂ component originating from this oxygen exists in the sintered body. For this reason, Si
O ₂ / in order to reduce the _{(Re 2 O 3 + SiO 2} ) molar ratio of either use less raw material powder having oxygen content, the Re ₂
It is necessary to increase the amount of O ₃ . However, there is a limit in reducing the total amount of oxygen in the raw material powder, and when the amount of Re ₂ O ₃ is increased, the amount of the grain boundary phase increases, and the mechanical properties and thermal conductivity decrease. cause. For this reason, the lower limit of the molar ratio of SiO ₂ / (Re ₂ O ₃ + SiO ₂ ) is 0.05.

The density of the silicon nitride sintered body of the present invention is preferably at least 95%, more preferably at least 97%. If the density of the sintered body is less than 95%, the amount of pores in the sintered body becomes too large, these become defects and cause a decrease in strength, and sufficient strength characteristics cannot be obtained. This is because phonons are scattered and the thermal conductivity is also reduced.

Further, in the silicon nitride sintered body of the present invention, the total content of Al, Be and Li in the sintered body is 2,000.
ppm or less, preferably 500 ppm or less. Al, Be, and Li form a solid solution in the silicon nitride particles during sintering. As a result, defects are formed in the silicon nitride particles, phonons are scattered, and the thermal conductivity is reduced. That is, A
If the contents of l, Be and Li exceed 2000 ppm, the solid solution amount of these elements in the silicon nitride particles becomes too large, and as a result, the thermal conductivity decreases.

In addition, yttrium in the silicon nitride based sintered body,
The contents of lanthanoid elements, Al, Be and Li are
After the sintered body is pulverized, it can be quantified by an atomic absorption method. For the total oxygen content in the sintered body, the sintered body is pulverized and an O / N simultaneous analyzer (TC-TC manufactured by LECO) is used. 436)
Can be quantified.

Further, the average particle diameter (short axis diameter) of the β-type silicon nitride particles in the silicon nitride sintered body according to the present invention is 0.1.
5 to 3 μm. Phonon, which is a heat transfer mechanism, easily propagates in silicon nitride particles and is scattered in the grain boundary phase. Therefore, as the size of each particle increases, the degree of phonon scattering by the grain boundary phase decreases, and the thermal conductivity improves. If the average particle diameter is less than 0.5 μm, the contribution of phonon scattering by the grain boundary phase increases, and it is difficult to obtain a sufficient thermal conductivity. on the other hand,
When the average particle diameter exceeds 3 μm, the thermal conductivity improves, but the coarsely grown silicon nitride particles become defects,
Mechanical properties such as strength are reduced.

Regarding the evaluation of the structure of the silicon nitride sintered body,
The silicon nitride-based sintered body is ground and further mirror-polished with diamond abrasive grains, then etched by high-frequency plasma in CF ₄ gas containing 8% of oxygen, and the obtained sample is scanned with a scanning electron microscope (SEM). Observe using). Next, regarding the quantitative evaluation of the structure, the obtained SEM photograph was used to quantitatively evaluate the number of particles at 300 or more by an image analyzer. The β-type silicon nitride particles had a hexagonal column shape, and the average particle diameter was a particle diameter corresponding to 50% of the particle diameter on the minor axis side.

The silicon nitride sintered body of the present invention having the above configuration has a thermal conductivity of 70 W / (m · K) or more. If the thermal conductivity is less than 70 W / (m · K), when used as a heat dissipation substrate or the like, sufficient heat dissipation characteristics cannot be obtained, and the use thereof is limited.

The mechanical properties of the silicon nitride sintered body according to the present invention are preferably such that the three-point bending strength is not less than 500 MPa and the fracture toughness is not less than 6 MPa · m ^1/2. . If the mechanical properties are lower than these values,
When used as a heat radiation board or an engine component, the mechanical properties become insufficient, and it may not be possible to use it for applications requiring high reliability.

Further, the silicon nitride sintered body of the present invention has a K phase (ReSi ₂ N), a J phase as a grain boundary crystal phase by X-ray diffraction.
Phase (Re ₄ Si ₂ O ₇ N ₄ ), H phase (Re ₁₀ Si ₇ O ₂₃
N ₄ ), Re ₂ Si ₃ O ₃ N ₄ , Re ₂ SiO ₅ and R
e ₂ O ₃ , K phase, J phase, H phase, Re phase
The sum of the main peak intensities of each of ₂ Si ₃ O ₃ N ₄ , Re ₂ SiO ₅ and Re ₂ O ₃ (I _GBB ) is the same as the peak intensity (I _SN ) of the (200) plane of β-type silicon nitride. 0.03
０．２0.20 is preferred. Incidentally, the identification of the crystal phase can be measured by an X-ray diffractometer as it is after grinding the sintered body.

The thermal conductivity of a silicon nitride sintered body is largely controlled by phonon scattering due to defects in silicon nitride particles and a grain boundary phase. Therefore, the thermal conductivity can be improved by crystallizing the grain boundary phase. Regarding the type of grain boundary crystal phase of the silicon nitride sintered body of the present invention,
Phase, H phase, Re ₂ Si ₃ O ₃ N ₄ , Re ₂ SiO ₅ and Re ₂ O ₃ . According to the study of the present inventors, regarding the thermal conductivity of a silicon nitride-based sintered body, when silicon nitride particles are dissolved and precipitated in a liquid phase, a liquid phase (yttrium and lanthanoid) having a composition in which oxygen is hardly dissolved in a liquid phase. It is effective to form a liquid phase having a high ratio of the oxide of the group III element), that is, X
2. The composition of a grain boundary crystal phase obtained by line diffraction,
Was found to be a compound that satisfies the composition (SiO ₂ / (SiO ₂ + Re ₂ O ₃ )) and that a composition in which silicon nitride was dissolved in these compounds was important for improving the thermal conductivity. Things.

In the silicon nitride sintered body of the present invention,
As noted, the grain boundary phase has crystallized above a certain value
And the degree of crystallization is K
Phase, J phase, H phase, Re_TwoSi_ThreeO_ThreeN_Four, Re_TwoSiO
_FiveAnd Re_TwoO_ThreeOf the main peak intensities (I
_GB) Is the peak intensity (I) of the (200) plane of β-type silicon nitride.
_SN) Is 0.03 to 0.20. I_GB/ I_SNBut
If it is less than 0.03, crystallization of the grain boundary phase is insufficient, and
Thermal conductivity may not be obtained, and high-temperature strength
, Etc., may also be reduced. one
One, I_GB/ I_SNExceeds 0.20, the amount of the grain boundary phase is large.
It becomes too hot and thermal conductivity and mechanical properties decrease
Sometimes.

Next, the method for producing a silicon nitride sintered body of the present invention is characterized in that the total content of Al, Be and Li is 2000 pp.
m or less, and the α ratio is 50% or less.
99 mol%, one or more selected from the group consisting of yttrium (Y) and lanthanoid group elements are 1 to 10 mol% in terms of oxide, and the oxygen content in the silicon nitride powder is SiO2.
Total _2-converted amount of SiO ₂ and SiO ₂ amount to be added is, the molar ratio of _{SiO 2 / (Re 2 O 3} + SiO 2) is added and mixed so that 0.05 to 0.5, 1 MPa or less nitrogen It is characterized by firing at a temperature of 1800 to 2000 ° C. in a pressurized atmosphere.

As impurities of the silicon nitride powder as a raw material, the total content of Al, Be and Li is 2000 ppm.
Or less, preferably 500 ppm or less. A
All of l, Be, and Li form a solid solution in the silicon nitride particles during sintering, thereby forming defects in the silicon nitride particles, and as a result, scatter phonons to lower the thermal conductivity. That is, if the content of Al, Be and Li in the raw material powder exceeds 2000 ppm, the amount of these elements dissolved in the silicon nitride particles during sintering becomes too large, and as a result, the thermal conductivity decreases. I will.

The α ratio of the silicon nitride powder is 50% or less, preferably 30% or less. If the α ratio exceeds 50%, a sufficiently dense sintered body cannot be obtained with the auxiliary composition of the present invention, and the thermal conductivity of the obtained sintered body may be reduced.

Next, as a sintering aid, silicon nitride powder 90
1 to 10 mol%, preferably 2 to 5 mol%, in terms of oxide of at least one selected from the group consisting of yttrium (Y) and lanthanoid group elements with respect to ~ 99 mol%.
Added. Since at least one oxide selected from the group consisting of yttrium (Y) and the lanthanoid group of the present invention does not form a solid solution with silicon nitride, when used as a sintering aid, the heat of the obtained silicon nitride-based sintered body is reduced. Effective for improving conductivity.
If the addition amount is less than 1 mol% in terms of oxide, the amount of liquid phase generated during sintering becomes insufficient, and a sufficiently dense sintered body cannot be obtained. On the other hand, the addition amount is 10 mol% in oxide conversion.
If the ratio exceeds the range, the amount of the grain boundary phase becomes too large, and the thermal conductivity decreases due to scattering of phonons in the grain boundary phase.
On the other hand, if the amount of the grain boundary phase is too large, mechanical properties such as strength and fracture toughness, particularly, high-temperature strength are reduced.

Further, the amount of oxygen in the silicon nitride powder is determined as SiO ₂
Regarding the converted SiO ₂ amount and the added SiO ₂ amount, the molar ratio of SiO ₂ / (Re ₂ O ₃ + SiO ₂ ) is 0.05 to 0.5, preferably 0.1 to 0.4.
It is. In the sintering of silicon nitride, silicon nitride particles grow while dissolving and precipitating in a grain boundary phase (liquid phase) composed of the added sintering aid and the raw material powder and the added SiO ₂ . In this case, when the amount of SiO _{2 in} the liquid phase increases, a part thereof forms a solid solution in silicon nitride particles precipitated from the liquid phase, and as a result, exists as defects in the silicon nitride particles and scatters phonons. As a result, the thermal conductivity is reduced. Therefore, as the composition of the grain boundary phase, the amount of oxygen belonging to Re ₂ O ₃ , which is obtained by converting one or more selected from the group consisting of yttrium (Y) and lanthanoid group elements from the amount of oxygen in the sintered body into oxides, is defined as The remaining portion was defined as SiO _2, and SiO ₂ / (Re ₂ O ₃
Making the molar ratio of (+ SiO ₂ ) 0.5 or less is effective for improving the thermal conductivity.

On the other hand, oxygen is inevitably contained in the silicon nitride powder, and S
An iO ₂ component is present. For this reason, SiO ₂ / (Re ₂
In order to reduce the molar ratio of (O ₃ + SiO ₂ ), SiO ₂
Use less raw material powder with less oxygen content,
It is necessary to increase the amount of Re ₂ O ₃ . However, there is a limit in reducing the amount of oxygen in the raw material powder, and when the amount of Re ₂ O ₃ is increased, the amount of the grain boundary phase is increased, which causes a decrease in mechanical properties and thermal conductivity. For this reason, SiO ₂ /
The lower limit of the molar ratio of (Re ₂ O ₃ + SiO ₂ ) is 0.05.

Next, the above composition is uniformly mixed by a ball mill or the like. The resulting mixed powder is subjected to cold isostatic pressing (CIP) after forming a mold to form a formed body. As for the molding method, there is no problem with a slurry casting method, an extrusion method, or the like other than the above method. Further, if necessary, a dispersant, a binder, and the like may be added.

Next, the obtained molded body is degreased as required, and then heated to a temperature of 1800 in a nitrogen pressurized atmosphere of 1 MPa or less.
It is fired at ２０００2000 ° C. for 1 to 48 hours to produce a sintered body. Regarding the firing temperature, if the temperature is 1800 ° C. or less, insufficient densification occurs. If the temperature is 2000 ° C. or more, the decomposition of silicon nitride occurs and the grain growth proceeds excessively, and the mechanical properties of the obtained sintered body deteriorate. Regarding the sintering temperature, preferably 18
50-1950 ° C. Regarding the firing time, if it is less than 1 hour, insufficient densification tends to occur, and firing for more than 48 hours is not economically advantageous. Regarding the firing atmosphere, nitrogen pressure is required at the firing temperature of the present invention in order to suppress decomposition of silicon nitride. The upper limit of the nitrogen pressure is preferably higher from the viewpoint of the physical properties of the obtained sintered body. However, when the nitrogen pressure exceeds 1 MPa, a special sintering device such as HIP is required, and there is a problem that the cost of the obtained sintered body becomes very high.

Further, the silicon nitride sintered body of the present invention can be used for a circuit board or the like which is required to have thermal conductivity, electrical insulation and mechanical properties. For example, in the case of a circuit board for a power module or the like, high heat transfer performance and mechanical properties have been required in addition to the electrical insulation properties required of the circuit board. The silicon nitride circuit board of the present invention has excellent mechanical properties such as strength and fracture toughness of a silicon nitride based sintered body as a base, and therefore has a high thermal stress such as a heat cycle and a bending stress on the board itself. Can have reliability. Further, since silicon nitride itself has a high insulation resistance, it is suitable for a circuit board used under severe use conditions. Further, the silicon nitride circuit board using the silicon nitride sintered body of the present invention is required to have not only excellent mechanical properties but also high thermal conductivity as compared with an alumina circuit board which is a general ceramic circuit board. Suitable for circuit board applications.

As a method of manufacturing such a circuit board,
After joining a plate-shaped silicon nitride-based sintered body or a silicon nitride-based sintered body processed into a plate shape by grinding or the like to a metal plate, a circuit can be formed by a technique such as etching and the like. Regarding the joining method of the silicon nitride-based sintered body and the metal plate, for example, a method of heating the silicon nitride-based sintered body and the metal plate in an inert gas or a vacuum atmosphere, and directly joining the sintered body and the metal plate (Direct joining method) or a brazing material made by mixing or alloying an active metal such as Ti or Zr with a metal such as Ag or Cu to form a low melting point alloy between the silicon nitride sintered body and the metal plate. It can be manufactured using a method of hot pressing in an inert gas or vacuum atmosphere (active metal method).

[0048]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Examples 1 to 17, Comparative Examples 1 to 8 To silicon nitride powders A to E having different powder properties as shown in Table 1, oxides having the composition shown in Table 2 were added, and methanol was further added. And wet-mixed in a wet ball mill for 5 hours. Next, these mixed powders were filtered and dried, and then molded in a mold at a molding pressure of 20 MPa.
A molded product of mx 30 mm x 50 mm was obtained. The obtained molded body was filled into a crucible made of boron nitride (BN), and sintered in an electric furnace of a carbon heater under the conditions of nitrogen gas pressure, firing temperature and firing time shown in Table 2 to produce a sintered body. did. In addition, the densities of the various sintered bodies obtained by the above operations were measured by the Archimedes method, and the results are shown in Table 3.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

Next, the obtained various sintered bodies were ground by a # 200 diamond wheel to obtain a surface of 20 mm × 20 mm.
It was processed into a shape of × 3 mm. Examples 1, 2, 10, 16
The crystal phases of Comparative Examples 7 and 8 were identified by X-ray diffraction using these processed bodies. Table 4 shows the results of the X-ray diffraction. In Comparative Example 5, the weight loss during firing was 50% or more, and a sintered body that could be used for subsequent evaluation was not obtained.

[0054]

[Table 4]

Next, these sintered bodies were ground, and a 10 mmφ × 3 mm disk for measuring thermal conductivity and a JIS-R
A strength test body according to the standard 1601 was prepared, and the thermal conductivity and the three-point bending strength at room temperature were evaluated. The thermal conductivity was measured by a laser flash method. Further, the strength test body was mirror-polished with diamond abrasive grains, and the fracture toughness was evaluated by the IF method according to JIS-R1607.

Further, after the mirror-polished sintered body was etched by high-frequency plasma at a power of 80 W for 2 minutes in a CF ₄ gas atmosphere containing 8% oxygen, SE
Observation (photographing) of the sintered body structure was performed using M. Next, using these SEM photographs, a quantitative evaluation of the sintered body structure was performed by an image analyzer. For the quantitative evaluation of each sintered body structure, the average particle diameter of each sintered body was measured using data of 300 or more silicon nitride particles. Table 5 shows the results.

A part of the test specimen used for the strength test was pulverized with a mortar and pestle made of silicon nitride, and the oxygen content was evaluated using an O / N simultaneous analyzer (TC-436) manufactured by LECO and the atomic absorption method was used. The quantitative evaluation of the content of the metal element was performed. Tables 3 and 5 show the obtained results.

[0058]

[Table 5]

[Examples 18 to 31] The compounds shown in Table 6 were mixed and molded in the same manner as in Example 1 to obtain a mixture of 5 mm ×
A 30 mm × 50 mm molded body was obtained. The obtained molded body is filled in a crucible made of boron nitride (BN), and is heated in a carbon heater electric furnace under a nitrogen pressurized atmosphere of 0.9 MPa.
It was fired at a temperature of 1900 ° C. for 8 hours to produce a sintered body. The obtained sintered body was evaluated for the composition, the amount of impurities, the sintered body density, the three-point bending strength, the fracture toughness, the average particle diameter, and the thermal conductivity in the sintered body in the same manner as in Example 1. went. Tables 7 and 8 show the obtained results.

[0060]

[Table 6]

[0061]

[Table 7]

[0062]

[Table 8]

The crystal phase of Example 18 was identified by X-ray diffraction. As a result, the K phase (Y ₄ Si ₂ O ₇ N) was obtained.
₇ and Yb ₄ Si ₂ O ₇ N ₇ ), Y ₂ O ₃ .Si
₃ N ₄ and Yb ₂ O ₃ .Si ₃ N ₄ were confirmed, and I _GB / I
_SN was 0.12.

[Example 32] Silicon nitride powder A: 97mo
1%, YF_Three: 4 mol%, Y_TwoO_Three: 1 mol%
And SiO_Two: The same method as in Example 1 with the addition of 3 mol%
Thus, a sintered body was produced. The density of the obtained sintered body is 98
%, And the amount of rare earth element in the sintered body is calculated as oxide
It was 2.5 mol%. Also, from the amount of oxygen in the sintered body,
The amount obtained by subtracting the amount of oxygen related to the amount of the rare earth element is taken as Si
O_TwoSiO in case of quantity_Two/ (Y_TwoO _Three+ SiO_Two)
Was 0.23.

Further, the three-point bending strength of the obtained sintered body was 6
90 MPa, the fracture toughness value was 6.6 MPa · m ^1/2 , and the thermal conductivity was 110 W / (m · K). The average particle size was 1.0 μm.

[Examples 33 and 34] In Example 33, the auxiliary mixed powder of Example 1 and Example 34 were molded in a mold at a pressure of 10 MPa, and then CIP molded at a pressure of 200 MPa. Thus, a molded product of 50 mm × 100 mm × 8 mm was obtained. These compacts were filled in a container made of BN, and fired in a carbon heater electric furnace at a temperature of 1900 ° C. for 8 hours under a nitrogen pressurized atmosphere of 0.9 MPa to produce a sintered body. The obtained sintered body is 40 m
It was a flat plate having a shape of mx 80 mm x 0.6 mm. The thermal conductivity of the obtained sintered body was 105 W / (m ·
K), and the value of Example 34 was 113 W / (m · K).

Next, an active metal-containing brazing material (Ag-Cu-Ti: 80-15-5) was applied to both surfaces of the silicon nitride
Screen printed with a thickness of 0μm, 0.3mm on the circuit side
A 0.15 mm thick copper plate is placed on the thick copper plate and
It was heated at a temperature of 850 ° C. for 30 minutes in a vacuum atmosphere of the order of 0 ⁻³ Pa. Thereafter, the mixture was cooled to obtain a composite. This composite was polished on the side of a copper plate having a thickness of 0.3 mm, printed with a resist for patterning, thermally cured, and then immersed and etched in an aqueous ferric chloride solution to form a pattern. Further, in order to remove the bonding material remaining between the circuits, the copper plate portion was immersed in an aqueous solution of ammonium ammonium fluoride, and then washed with water to produce a circuit board having a pattern formed thereon.

Next, the circuit board is placed in a lower span of 30 m.
When the three-point bending strength at m was measured, Example 33 was 7
It was 50 MPa, and Example 34 was 730 MPa. In addition, 3000 heat cycle tests were performed in a temperature range of -40 ° C to 150 ° C. The three-point bending strength of the substrate after the heat cycle test was 700 MPa in Example 33 and 690 MPa in Example 34, and no cracks between the circuits or peeling of the circuits were recognized even after the heat cycle test.

Example 35 Two types of copper plates having different thicknesses used in Example 33 were placed on both surfaces of the silicon nitride flat plate of Example 33, and heat-treated in a nitrogen gas atmosphere at a temperature of 1050 ° C. for 5 minutes. Then, cooling was performed to produce a composite. From the obtained composite, a circuit board was produced in the same manner as in Example 33. The three-point bending strength of the obtained circuit board is 730MP.
a, and the three-point bending strength after 3000 heat cycles was 670 MPa. Also, no cracks between circuits or peeling of circuits were observed after the heat cycle test.

Example 36 To a powder obtained by mixing the sintering aid of Example 1, 20 parts by weight of Serander (manufactured by Yuken Industries) and 20 parts by weight of pure water were added and mixed as a molding binder, followed by extrusion molding. A sheet having a sheet width of 100 mm and a sheet thickness of 0.8 mm was produced by a machine. The resulting sheet is 45
The sheet was cut into a size of mm × 90 mm, BN powder was applied to the surface, and 10 sheets were laminated, and degreased in air at a temperature of 550 ° C. for 2 hours. Next, the obtained degreased body was filled in a BN container, and fired at a temperature of 1900 ° C. for 8 hours in a nitrogen pressurized atmosphere of 0.9 MPa in an electric furnace of a carbon heater to produce a sintered body. The obtained sintered body was dry-honed using # 400 alumina abrasive grains to remove BN and altered layers on the surface. The thermal conductivity of the obtained sintered body is 104 W / (m · K)
Met.

Next, a circuit board was manufactured using the silicon nitride flat plate in the same manner as in Example 33. The three-point bending strength of the obtained circuit board was 740 MPa, and the three-point bending strength after 3000 heat cycles was 700 MPa. Further, even after the heat cycle test, cracks of the substrate between the circuits and peeling of the substrate from the circuit were not recognized.

[0072]

The silicon nitride sintered body of the present invention controls the composition, amount and crystallinity of the grain boundary phase by reducing the amount of impurities dissolved in the silicon nitride particles during sintering. Therefore, it has excellent mechanical properties such as strength and fracture toughness, and has a thermal conductivity of 70 W /
(M · K) or more, it can be used as a material for various structural parts in a wide range of fields such as insulating substrates for semiconductors, automobiles, machinery and the like. Furthermore, the method for producing a silicon nitride-based sintered body of the present invention uses the above-described silicon nitride-based sintered body having excellent thermal conductivity and mechanical properties at a low cost without using a special sintering method such as HIP. Can be manufactured. Also,
Since the silicon nitride circuit board of the present invention has high thermal conductivity and excellent mechanical properties, it is a circuit board suitable for use in transportation equipment and the like requiring reliability and a circuit board for a power module. .

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hiroshi Yokota 3-5-1 Asahicho, Machida-shi, Tokyo Denki Kagaku Kogyo Co., Ltd.

Claims (4)

[Claims] 1. Silicon nitride (Si ₃ N ₄ ) 90-99 mo
l%, yttrium (Y) and oxides of one or more selected from the group consisting of lanthanoid elements (Re ₂ O ₃₎ containing 1 to 10 mol% in terms of, Re ₂ O from the total oxygen content in the sintered body When SiO ₂ is the balance excluding the oxygen amount attributed to ₃ , the molar ratio of SiO ₂ / (Re ₂ O ₃ + SiO ₂ ) is 0.05 to 0.5, and the average particle diameter of the silicon nitride particles (Average short axis diameter) 0.5 to 3 μm, A in the sintered body
A silicon nitride-based sintered body characterized in that the total content of l, Be and Li is 2000 ppm or less and the thermal conductivity is 70 W / (m · K) or more. 2. K phase as a grain boundary crystal phase by X-ray diffraction
(ReSi_TwoN), J phase (Re_FourSi_TwoO₇N_Four), H
Phase (Re_TenSi₇O_{twenty three}N_Four), Re_TwoSi_ThreeO_ThreeN_Four,
Re_TwoSiO_FiveAnd Re_TwoO_ThreeAt least one of
Contains, K phase, J phase, H phase, Re_TwoSi_ThreeO_ThreeN_Four, R
e_TwoSiO_FiveAnd Re_TwoO_ThreeEach main peak intensity
Sum of (I_GB) Is the peak of the (200) plane of β-type silicon nitride.
Strength (I _SN) To 0.03 to 0.20
The silicon nitride-based sintered body according to claim 1, wherein: 3. The total content of Al, Be and Li is 20.
To 90 to 99 mol% of silicon nitride powder having an α ratio of 50 ppm or less and at least one selected from the group consisting of yttrium (Y) and a lanthanoid group element in an amount of 1 to 10 mol% in terms of oxide, the total oxygen amount in terms of SiO ₂ was SiO ₂ amount and SiO ₂ amount to be added in the powder is added such that the molar ratio of _{SiO 2 / (Re 2 O 3} + SiO 2) is 0.05 to 0.5 Mix, 1MPa
3. The method for producing a silicon nitride-based sintered body according to claim 1, wherein the sintering is performed at a temperature of 1800 to 2000 [deg.] C. in a nitrogen pressurized atmosphere of less than 1. 4. A silicon nitride based circuit board comprising the silicon nitride based sintered body according to claim 1 or 2.